Anyone try advancing SC cams beyond 1.7mm?

[boosted79]

Spent some quality time today with the DI and degree wheel. SC cams presently set at 1.72 mm lift on overlap. I have 1.7mm intake valve to piston clearance vs. 1.5 mm minimum recommended so I have some room to play with. Has anyone tried running with these cams set 1.8 or 1.9 mm lift on overlap? '79 3.3 CIS 930 stock pistons, heads with headers, turbo,IC

[smurfbus]

I run 964 cam with 1.96mm if that gives any help.

[boosted79]

Thanks, I should have said I'm CIS, you are running those cams quite advanced but you are EFI. Right now at 1.72mm the intake is opening at 8 deg BTDC. I'm building this for low to mid-range so thinking about advancing timing even more but not sure the CIS will like it. I'm going to advance it to 2 mm and see what it does to intake opening and what I have for p to v clearance.

[boosted79]

Set the cam at 2.0 mm on overlap, it moved the intake opening up to real close to 10 deg BTDC ( this is using the euro std of 1mm lift to determine open/close points). Set the intake lift to 2.0 mm and it swung thru fine, no p to v contact. Yesterday I was feeling the exhaust rocker starting to come up the ramp and was interpreting that as p to v interference. I have to check the ex cam next for opening/closing points and p to v clearance. the question is where to go with this? I have to do some research. Enough for today, going to watch the hydroplane races.

[smurfbus]

Im cis too. I just have some refinements to control the control pressures of the wur. I tried over 2mm but it did not have enough clearance.

My pre boost running is imo very good.

[boosted79]

Really? Good info, thanks. Does it idle ok? Maybe I can figure out where your 964 is opening at 1.96 mm and compare to where I am now.

[RarlyL8]

We've cranked the SC cams past 1.70 but not past 2.0. The compromise was to get max low end without loosing too much up top using a K27-7200.

[smurfbus]

Idles just fine. No ill efects at all.

[boosted79]

RarlyL8 - how did it run at 2.0? I can't relate to this lift at overlap stuff, need to determine what intake and exhaust center lines are at these various settings to understand where I am with timing.

[RarlyL8]

We have a master mechanic that has forgotten more than I'll ever know about these engines and how to make magic with them. I don't know what the max advance is for the SC cams only what works best for our builds. Key is to find the sweet spot so the components you have chosen work best together.

[boosted79]

Here are some numbers that I came up with today, all with .1 mm lash. These are at the euro std. of 1 mm lift.

mm intake lift
at TDC overlap ..............in.opens..............in.closes..... ........ex.open..........ex.close

1.7 ................................7.5 btdc ............45.5 abdc..........47.5 bbdc...........6.5btdc

2.0 ................................9.5 btdc.............43.5 abdc..........49.5 bbdc...........8.5 btdc

2.3 ..............................12.5 btdc ............40.5 abdc..........52.5 bbdc..........11.5 btdc

The bump from 1.7 to 2.3 picks up some nice advance but it may be too much with intake opening at 12.5 btdc.

[Mr9146]

2.0 is the farthest I've pushed them.

[boosted79]

I ran those intake closing points thru a dynamic CR calculator for this engine running .9 bar and the change from 1.7 to 2.3 gives an increase in dynamic CR of only .17. What these engines need is a solid roller to slam the valves open and close now.. Will probably set it at 1.9, too much screwing around with this for a street car.

[boosted79]

I set them at 1.9. My reasoning is the Gruppe B intakes open at 11, 1.9 gives close to 9.5 deg BTDC opening on these cams. The saying in the NA world is you have too much advance cranked in when the intake hits the piston, LOL, not quite the same in a turbo though. Opening the ex. a little earlier should help light the turbo lower also.

[krasuskyp]

I went 1.6 per the recommendation of many of the big name / legit gurus here... kindasorta wishing I'd ticked a shade more. Ah well 8-)

[boosted79]

Once I get it together I'll get it on the dyno. I want mid range torque, going with a smallish turbo, probably BW S200SX-E.

[Speedfab]

Originally Posted by boosted79

Once I get it together I'll get it on the dyno. I want mid range torque, going with a smallish turbo, probably BW S200SX-E.

Let me know if you need the hookup.

[boosted79]

LOL, maybe I can use that on my 850 Commando.